The presently disclosed subject matter relates to a pulse photometer.
A pulse photometer is an apparatus which irradiates the living tissue of the subject with light beams at a plurality of wavelengths having different light absorption properties of a light absorption material in blood, and which measures the intensities of the light beams at the wavelengths transmitted through or reflected from the living tissue, thereby calculating the concentration of the light absorption material in blood. The intensities of the light beams are acquired in the form of a pulse wave signal corresponding to the absorbance which is changed in accordance with the pulsation of the blood. Japanese Patent No. 4,196,209 discloses a technique in which, in order to reduce noises from a pulse wave signal, the affine transformation is performed by using a known absorbance ratio (a ratio of absorbances at wavelengths).
In the technique disclosed in Japanese Patent No. 4,196,209, the result of a past measurement in which it was determined that there is no noise contamination is used as the known absorbance ratio. In the case where the absorbance ratio obtained from a pulse wave signal, and that obtained from a noise signal have similar values, however, there is a possibility that the absorbance ratio in the noise signal is employed as the known absorbance ratio. When such erroneous employment occurs, the subsequent noise removal process relies on a value based on the noise signal, and therefore the calculation of the concentration of the light absorption material in blood may lack accuracy.
Therefore, it is an object of the presently disclosed subject matter to improve the accuracy of the calculation of the concentration of a light absorption material in blood.